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    ASTM E517 - 19

    Méthode d’essai standard pour Rapport de contrainte plastique r pour la tôle

    Active Standard ASTM E517 Developed by Subcommittee: E28.02

    Book of Standards Volume: 03.01


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    Significance and Use

    4.1 The plastic strain ratio r is a parameter that indicates the ability of a sheet metal to resist thinning or thickening when subjected to either tensile or compressive forces in the plane of the sheet. It is a measure of plastic anisotropy and is related to the preferred crystallographic orientations within a polycrystalline metal. This resistance to thinning or thickening contributes to the forming of shapes, such as cylindrical flat-bottom cups, by the deep-drawing process. The value of r , therefore, is considered a measure of sheet-metal drawability. It is particularly useful for evaluating materials intended for parts where a substantial portion of the blank is drawn from beneath the blank holder into the die opening.

    4.2 For many materials the plastic strain ratio remains essentially constant over a range of plastic strains up to maximum applied force in a tension test. For materials that give different values of r at various strain levels, a superscript is used to designate the percent strain at which the value of r was measured. For example, if a 20 % elongation is used, the report would show r20.

    4.3 Materials usually have different values of r when tested in different orientations relative to the rolling direction. The angle of sampling of the individual test specimen is noted by a subscript. Thus, for a test specimen whose length is aligned parallel to the rolling direction, plastic strain ratio, r , is reported as r0. If, in addition, the measurement was made at 20 % elongation and it was deemed necessary to note the percent strain at which the value was measured, the value would be reported as r020.

    4.4 A material that has an upper yield strength (yield point) point followed by discontinuous yielding stretches unevenly while this yielding is taking place. In steels, this is associated with the propagation of Lüders' bands on the surface. The accuracy and reproducibility of the determination of plastic strain ratio, r , will be reduced unless the test is continued beyond this yield-point elongation. Similarly, the discontinuous yielding associated with large grain size in a material decreases the accuracy and reproducibility of determinations of plastic strain ratio, r , made at low strains.

    1. Champ d'application

    1.1 Cette méthode d’essai couvre les essais de traction spéciaux pour la mesure du rapport de déformation plastique, r, de la tôle destinée aux applications d’emboutissage profond.

    1.2 Les valeurs indiquées en unités pouce-livre doivent être considérées comme standard. Les valeurs données entre parenthèses sont des conversions mathématiques d’unités SI qui sont fournies à titre informatif seulement et ne sont pas considérées comme standard.

    1.3 Cette norme ne traite pas de l’ensemble des préoccupations potentielles en matière de sécurité concernant son utilisation. L’utilisateur de cette norme est responsable d’appliquer les pratiques en matière de santé et sécurité et de définir les conditions d’application des limites réglementaires avant son utilisation.

    1.4 Cette norme internationale a été développée conformément aux principes internationalement reconnus de normalisation établis dans le cadre de la Décision sur les principes devant régir l’élaboration de normes, guides et recommandations internationaux émise par le comité sur les obstacles techniques au commerce (OTC) de l’Organisation mondiale du commerce.

    2. Documents de référence